This invention relates to audio recording/reproducing apparatus and, more particularly, to such apparatus wherein redundant information, namely, pauses, included in audio signals are removed, thereby eliminating the need to record non-informational signals; but such redundant information is re-inserted during a playback operation.
In typical prior art dictation systems, audio information is recorded on a magnetic medium, typically magnetic tape, wherein virtually all of the sounds and pauses uttered by a dictator are recorded and subsequently played back. Typical of such dictation equipment are analog recorders wherein the audio information is recorded in analog form. Customarily, analog dictation systems have been classified as stand alone units, also known as desk-top or portable recorders in which the magnetic tape is housed in a replaceable tape cassette, central systems wherein one or more bins of endless tape are accessible to several dictators and to several transcriptionists, whereby multiple dictate and transcribe operations may be performed simultaneously, central systems wherein individual tape decks are used in place of the aforementioned tape bins, and so-called small work group systems which combine the advantages of both central and stand alone dictation systems. Each of the aforementioned types of equipment has been made available by Dictaphone Corporation, the assignee of the present invention, and descriptions of typical apparatus are found in the following patent literature:
Stand alone machines are described in U.S. Pat. Nos. 4,378,577 and 4,410,923.
Central systems using endless magnetic tape as the recording medium are described in U.S. Pat. Nos. 3,817,436 and 3,984,644.
Central systems using replaceable tape cassettes are described in U.S. Pat. Nos. 4,092,679 and 4,636,888.
Small work group systems are described in U.S. Ser. No. 145,228, filed Jan. 19, 1988 and U.S. Ser. No. 799,909, now U.S. Pat. No. 4,722,077 filed Nov. 20, 1985.
Recently, digital recording techniques have been proposed for use in dictation equipment. Although digital controls have long been used in controlling and monitoring dictation and transcription operations, such as described in U.S. Pat. Nos. 4,319,337 and 4,623,988, the audio information recorded in such digitally controlled equipment nevertheless has been recorded in analog form. However, with the recent development of low cost, high capacity digital storage equipment, such as high capacity floppy disks and, more advantageously, high capacity hard disk storage systems (also known as Winchester disk drives, rigid disk drives, disk packs, etc.), the opportunity to economically record audio information in digital form has been made available.
In digital dictation equipment, input analog audio signals are sampled and each analog sample is converted to a digital audio sample. Bytes representing the digital audio samples are recorded on a magnetic disk, either a floppy disk or a Winchester disk, in much the same way as any other digital information is magnetically stored (or "written"). During playback (or "reading"), each byte is read from the magnetic disk and converted to an analog sample. Successive samples result in a restoration of the original analog audio signal. The high speeds at which digital signals are processed, recorded, read and manipulated when compared to the relatively low frequencies of typical speech signals, permit a relatively inexpensive digital storage device to be used as the primary store of a central dictation system. By using a single (or relatively few) high capacity Winchester disk drive, several dictators and several transcriptionists may access the central store to record and transcribe messages. Also, digital recording techniques permit quick access, on the order of milliseconds, to virtually any message that has been recorded, thereby facilitating quick review, recovery and editing of respective messages. Indeed, contrary to typical analog dictation systems, a digital system permits a dictator to edit a message in such a way that, during transcription of that edited message, the transcriptionist need not even be aware of the fact that editing has been achieved. This contrasts with conventional analog dictation systems wherein editing typically is achieved by recording special instructions to direct a transcriptionist to other parts of the magnetic tape on which inserts or other changes are recorded.
One drawback in audio recording systems has been the need heretofore to record redundant, or non-informative, signals. In a typical audio message, several pauses are present between syllables, words and phrases. Some of these pauses are inherent in typical speech patterns, and others merely are a function of the dictator's need to collect his thoughts while recording a message. In any event, when such pauses are recorded, they occupy useful space on the recording medium which could otherwise be occupied by intelligible sounds.
There have been attempts heretofore to minimize the recording of pauses on the record medium by using so-called voice operated equipment (VOX) whereby a recording operation commences at the first utterance of audible sound, but that operation is interrupted when a predetermined amount of silence, or a pause, is detected. While such VOX recorders generally have been successful in analog dictation systems, they still result in the recording of significant amounts of redundant information in digital dictation systems. It is desirable to eliminate pauses in audio signals to a much greater extent than has been achieved by conventional VOX systems. It also is desirable to provide flexibility in re-inserting pauses when audio signals which had been compressed as a result of pause removal are played back.
Although digital recording/playback systems provide a desirable quality of high fidelity, if audio signals are recorded in compressed form (as by removing pauses therein), the reinsertion of such pauses, even if of a selectively variable length, nevertheless results in high fidelity "dead silence". Upon hearing such "dead silent" pauses, a transcriptionist may believe that the transcription equipment is not operating properly. It is further desirable to minimize such erroneous suspicions of equipment malfunction; and this is achieved by the invention disclosed herein.